1. Technical Field
The present invention relates generally to transmission of data from ports associated with an output adapter in a date transmission network such as an asynchronous transfer mode (ATM) network. In particular the present invention relates to a device for selecting multi-rate ports in accordance with their respective transmission rates.
2. Description of the Related Art
Advancing semiconductor technology evolution has produced high networking protocol engines within switching nodes of a data transmission network such as an ATM network. In ATM broadband networking technology, the current designed transmission rate is in the range of 2.5 Gigabits/s in support of high speed intermediary devices such as the OC48 physical interface.
High-capacity network engines may be utilized to process traffic from higher rate ports as well as being shared by several lower rate ports. For example, existing protocol engines that are designed to support an OC12 port (622 Mbps) can also process the traffic from four OC3 ports. The higher the processing capacity, the higher the number of port combinations that can be supported. In practice, an OC48 protocol engine could support one OC48 port or four OC12 ports or sixteen OC3 ports or mixed combination such as one OC12 and twelve OC3, or three OC12 and four OC3.
Providing such flexibility to the customer is advantageous for a customer who may not necessarily require a sixteen OC3 port adapter. In addition, the multi-port approach permits a reduction in switching equipment cost since an integrated protocol engine is shared by several ports.
In practice, an engine that is capable of processing 2.5 Gbps of ATM traffic is also capable of processing a 15 53 byte ATM cell every 169.6 ns. On the adapter receive side of the engine, the aggregate flow received is simply composed of the flows received on the various ports. In this context, a multiplexer logic device is utilized to feed the protocol engine with the traffic from the various ports of the input adapter. The only constraint for the input traffic is that the sum of the port rates must be lower than the engine processing capacity.
On the transmit side (output adapters), the problem is very different. As for the receive side, the protocol engine receives traffic from the switching fabric of the switching node at the aggregate rate and processes this traffic: flow identification such as the lookup of the ATM label, flow classification with respect to the traffic class priorities, congestion management, and finally queuing of the incoming cell in the appropriate queue. Once this process is completed, the outgoing traffic must then be sent over the various ports attached to the output adapter. This means that the processing power of the protocol engine must be shared between the ports.
For a case in which there is a single port, or in for cases in which all ports have an equal transmission rate, the design goal is simply to sharing the outgoing traffic equally among the various ports. Assuming, however, that the ports comprise a mixed configuration consisting of, for example, one OC12 port and twelve OC3 ports, an equal share of the aggregate rate of 2.5 Gbps provides to each port a service requirement of 2.5 Gbps/13=192 Mbps. Such a rate is too high for an OC3 port which has a capacity of 155 Mbps, and too low for the OC12 port which has a capacity of 622 Mbps.
Furthermore, it may be necessary for a switching node to be able to control the rate at which the traffic is sent over a physical port practically transmitted at a programmable rate lower than the physical rate of the port. This can be practically the case when the rates in the network backbone such as E2 or E3 links are lower than the access rates of the ports (for example OC3).
It would therefore be useful to provide a system and method for distributing output traffic from a high capacity network engine to multiple multi-rate ports in a distributed manner such that the maximum output rate of the engine is realized without overloading individual output ports.
A system and method for selecting one port among multiple output ports having various transmission rates attached to an output adapter of a switching node in a data transmission network and enabling it to transmit its data over the network are disclosed herein. The system of the present invention includes a storage device that contains a list of identification codes for the ports. The identification code list is arranged in a prioritized order from the port having the highest transmission rate to the port having the lowest transmission rate. The system further includes port service request means that generate a service request signal for each port, wherein the service request signal has a frequency corresponding to the transmission rate of the object port. Port selection means are utilized to, in response to said identification codes and said service request signal, select a requesting port having a highest priority according to its identification code and enabling the selected port to transmit data over the date transmission network.
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.